Methodological Issues and Results of Experimental and Computational Studies of Critical Heat Flows in RITM-200 Reactor Fuel Assemblies for Small NPP

Experimental studies of critical and post-crisis heat transfer, performed on electrically heated models of different modifications of cassette-core fuel assemblies, that can be used to justify the heat-engineering reliability of the RITM-200 reactor core for small NPP are presented. The characteristics of the testing stand, assemblies, and experimental techniques are given, and the nature of the origin and development of the crisis over the cross section of assemblies are described. Comparative assessments are made of the effect of changes in the operating parameters, energy release length, and the number of heated elements on the critical power. Justification is given for the conservatism, due to the absence of a heat-conducting core in fuel-rod simulators in the experimental assemblies, of the method used to determine the post-crisis power resources. Recommendations are made for further studies of critical heat flows in justification of the design characteristics of the RITM-200 reactor core in small NPP.